Modulated wave shaper



DE AWITT R. GODDARD MODULATED WAVE SHAPER INVENTOR.

BQ EW|T`T EUDDARD Arron/Vey Patented Apr. 26, 1949 MODULATED WAVE SHAPER De Witt Rugg Goddard, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application February 28, 1945, Serial No. 580,211

(Cl. Z50-36) l' 8 Claims.

This invention relates to wave shaping circuit arrangements, and more particularly to a modulated wave shaper.

An object of my invention .is to provide a modulated wave Shaper which has a limiting action Without loss of the amplitude modulation characteristic.

Another object is to provide means for squaring olf the peaks of a modulated wave at varying amplitude levels thereby ,-to produce an amplitude modulated wave which in some degree resembles a rectangular wave and is, therefore, rich in harmonics.

Still another object is to provide a low distortion harmonic generator suitable for deriving harmonics of a modulated wave which may be separated from the fundamental frequency components of such a wave.

The present invention has as an object, a method and means of overcoming certain difficulties encountered in the use of my MUSA system as described in U'. S. application #695,893, filed September 10, 1946; In vsaid application, the requirement is to produce harmonics of an amplitude modulated radio frequency signal. Ordinarily, if a radio frequency signalis subject to limiting so as to give a distorted form to the sine wave, this wave will be rich in harmonics. However, any normal formv of'limiting will, of course, remove amplitude modulation. In the present application-f1 disclosel a special type of limiter which-provides thev distorted wave form rich in harmonics andyet preserves the amplitude modulation. In my multiple unit steerable antenna system, disclosure referred to above, it is necessary to usesome harmonic of a fundamental frequency. An ordinary harmonic generator may be used for this purpose for on-oiT telegraphy phase modulation, frequency modulation, frequency shift keying and so forth but it is not satisfactory for amplitude modulated signals. The-improved harmonic generator of the present invention is satisfactoryv for deriving harmonics of amplitude modulated signals without distorting the amplitudemodulation. The essence of theinvention itself resides in the novel construction of its circuit arrangement and in the method of wave' shaping which is herein shown an-d described'. It issu'icient, therefore, for the purposesof this specification to show how a modulated wave having the usual characteristics of a modulated sine wave may be applied as input energy tothe circuit arrangement which I believe to be novel, 'and how this wave, after shaping, may be delivered to a plurality 'of band pass filters for segregating the fundamental frequency components and one or more harmonic frequency components.

My invention will now be described in more detail, reference being made to the accompanying drawing in which Fig. 1 shows a preferred circuit arrangement for carrying out the invention;

Fig. 2 shows graphically a representation of a modulated wave of ordinary sine wave formation;

Fig. 3 shows graphically a -derivative of the wave illustrated in Fig. 2 but now shaped with substantially rectangular peaks, such a wave being well known to possess a richness of harmonies; and

Fig 4 shows graphically a second harmonic derivative of the original wave.

Referring first to Fig. 1, I show therein two input terminals l across which the potentials of a modulated wave such as shown in Fig. 2 may be'impressed. One of the terminals I is directly connected to the control grid in an amplier tube 2. The same terminalA is also connected to one terminal of a potentiometer 3, the other terminal of which is grounded. The second of the input terminals I is also grounded- A detector tube 4 possesses La control grid which `is directlyv connected to a tap on the potentiometer 3. By varying theV position of the tap on the potentiometer 3 the amplitude of the signals delivered in the output circuit of tube 4 may be varied with respect to the amplitude of corresponding signals delivered in the output circuit of the tube- 2. In other respects, however, the output current from tube 2 is characterized as a modulated radio frequency wave, while the output from tube il consists essentially in detected audio frequency components capable of being transformed in the audio frequency transformer 6. Positive anode potentials are supplied to tubes 2 and 4 from any suitable source of direct current having a grounded negative terminal. The anode in tube 4 is coupled to ground through a radio frequency bypass condenser l2.

Connected to each of the cathodes inthe tubes 2 and Il are cathodelresistors 8, each -of which is shvunted by a capacitor 9.' Thelcathode circuit impedances are grounded.

In the output circuit of tube 2 I have included the primary winding of a radiofrequency transformer 5, while in -the output'circuit of the tube 4 I have includedi the primarywinding of a relatively low frequency transformer' 6, suitabley for translating', the modulation frequency -com-p'o- 3 nent of the signals with attenuation of the high frequency component.

Transformer 5 has a secondary winding the terminals of which are connected respectively to one and the other of two anodes in a twin diode rectifier tube 7. The two cathodes of this tube are inter-connected and are grounded.

A mid-tap on the secondary winding of transformer 5 is connected to the grounded cathodes of tube 'I through a resistor IB. This resistor is shunted by a capacitor II. The mid-tap on the secondary of transformer 5 is also connected to one terminal of the secondary winding on transformer The other terminal of the secondary on transformer 6 is connected to a tap on a potentiometer I3 which in turn is connected across the terminals of a biasing battery or other direct current source Ill. The positive terminal of this source is grounded so that the anodes in tube 'I may be more or less negatively biased with respect to ground, thus rendering this tube unresponsive to signal currents below a certain critical amplitude level.

The anodes of tube l are connected respectively to two primary winding terminals on a transformer 2|. The secondary winding of this transformer has a grounded center tap, and its terminals are connected respectively to one and the other of two control grids in a twin triode tube I5. The common cathode of tube I5 is connected to ground through a cathode resistor It, this resistor being shunted by a capacitor Il.

Tube I5 is arranged to operate as a push-pull radio frequency amplifier. The two anodes are connected respectively to the terminals of a primary winding in a radio frequency output transformer I8. A mid-tap on the primary winding of transformer I8 is fed with direct current of suitable positive potential for operating the tube I5. The source of operating potential has a grounded negative terminal. The secondary winding of transformer I8 has its terminals connected to a plurality of radio frequency band pass filters such as I9 and 20. Additional filters may be supplied if desired. The band pass characteristics of these filters are so chosen as to provide at least a separation between the fundamental frequency output and the harmonic frequency output from the push-pull amplifier tube I5.

If separation is desired between harmonics of one order and harmonics of another order, such can readily be had by the use of additional band pass filters, as may be well understood by those skilled in the art.

The operation of my modulated wave Shaper may be illustrated by considering that the input energy supplied to the terminals I is, for eX- ample, a modulated carrier wave having a carrier frequency of, say, 100 kilocycles. The signal passes to the amplifier 2 and detector 4. The output from tube 2 possesses both carrier frequency and modulation frequency components. The modulation frequency component from detector tube 4 is selected, the carrier wave component being substantially suppressed.

The variable potentials of the modulation wave as transformed through the transformer 6 are added algebraically to the D. C. bias potential of the tap on potentiometer I3, the resultant potential being impressed across the resistor I0 which produces a variable bias upon the anodes of the tube 1. The variations of bias are synchronized with the modulation amplitude variations detected in the twin diode tube 1.

4 The effect is, therefore, to clip the peaks of the waves applied to the push-pull amplifier I5 and to square them off. The variability of amplitude is, however, preserved.

As before stated, the output from the tube I5 will be recognized as one which is rich in harmonies and is, therefore, capable of utilization either for its harmonic frequency components or for purifying the fundamental frequency components which may be separated therefrom. The fundamental frequency characteristic of the output as passed through the band pass filter 20 would appear as shown in Fig. 3.

The band pass filter I9 may be so characterized as to deliver one or more selected harmonics. If, for example, the second harmonic alone is wanted, then its output would appear as graphically shown in Fig. 4.

It will be understood that modifications of my invention may be made by those skilled in the art without departing from the spirit and scope of the invention itself.

I claim:

1. In a signaling system the method of generating harmonic wave components of an amplitude modulated wave which comprises limiting the amplitudes of the wave peaks of the original wave, conforming the limited wave peaks to an envelope which simulates the modulation envelope of the original wave, and filtering the limited wave to separate said harmonic wave components from the fundamental frequency components thereof.

2. In apparatus of the class described, an electronic amplifier and an electronic detector, input circuits for said amplifier and detector connected to a common source of amplitude modulated waves, a full-Wave rectier stage coupled to the output side of said amplifier, said rectifier stage comprising a pair of diode discharge devices having independent anodes and interconnected cathodes, a single resistive impedance and divided coupling means forming a Y-connection between the cathodes and the anodes, and means for varying the potential gradient across said resistive impedance as a function of the output energy from said detector.

3. Apparatus according to claim 2 in combination with filtering means arranged and adapted to segregate in different channels thefundamental frequency components of said modulated waves and the harmonic frequency components thereof.

4. In a system for generating harmonic frequencies of varying amplitudes which conform substantially to the modulation envelope of a modulated fundamental frequency wave, a multistage translating circuit including an amplifier, and a twin diode detector, a transformer intercoupling the output side of said amplifier and the input side of said detector, a resistor connecting a neutral tap on the secondary of said transformer with the two cathodes in-said detector, the terminals of said secondaryibeing separately connected to one and the other of the anodes in said detector, a capacitor in shunt with said resistor, a triode detector stage having an input circuit common to the input circuit of said amplifier, and means responsive to amplitude variations in the output from said triode detector for varying the potential gradient across said resistor, thereby to develop output waves from said twin diode detector which are rich in harmonicsand which conform closely to the modulation envelope of the original wave.

5. A system according to claim 4 and including parallel connected band pass filters for segregating different frequency components of the output energy derived from said twin diode detector, one of said filters being characterized for passing fundamental frequencies Within a predetermined band and another of said filters being characterized for passing a predetermined lband of harmonic frequencies.

6. The method of producing complex alternating current energy comprising components integrally related to a fundamental frequency including these steps, limiting the peak amplitudes of a first portion of amplitude Narying wave energy of said fundamental frequency to derive wave energy of rectangular wave form, rectifying a second portion of said amplitude varying wave energy of said fundamental frequency, and modifying the rst mentioned limiting action in accordance with the amplitude varying components derived by rectifying said second portion of wave energy to derive wave energy of rectangular Wave form and of varying amplitude which is rich in harmonics.

7. The method of producing energies of frequencies integrally related to a fundamental frequency which includes these steps, limiting the peak amplitudes of a first portion of amplitude varying wave energy of said fundamental frequency to derive wave energy of rectangular wave form, rectifying a second portion of said amplitude vadying wave energy of said fundamental frequency, modifying the first mentioned limiting action in accordance With the amplitude variations of said wave energy derived by rectifying the same to derive wave energy of rectangular wave form and varying amplitude which is rich in harmonics, and selectively separating energies of the fundamental and harmonic frequencies appearing in said limited wave energy of varying amplitude as desired.

8. In apparatus of the class described, an electron discharge tube amplifier and an electron discharge tube detector, input circuits for said amplifier and detector coupled to a common source of amplitude varying wave energy, a third electron discharge tube having electrodes in an alternating current input circuit and in an alternating current output circuit, a coupling between the last input circuit and the output of said amplier, a utilization circuit coupled with said alternating current output circuit, a biasing circuit for said third tube including a direct current impedance :between electrodes thereof and a coupling between the output of said detector and said impedance.

DE WITT RUGG GODDARD.

REFERENCES CITED The following references are of record in the file of this patent:

UNTTED STATES PATENTS Number Name Date 1,885,728 Keith Nov. 1, 1932 1,931,870 Kramer et al. Oct. 24, 1933 2,038,570 Keall Apr. 28, 1936 2,144,995 Pulvermacher Jan. 24, 1939 2,343,207 Schrader Feb. 29, 1944 2,345,026 Boykin Mar. 28, 1944 FOREIGN PATENTS Number Country Date 106,898 Australia Mar. 23, 1939 

